RTAI. Antonio Barbalace (modified by M.Moro 2011) RTAI

DEI Universit y of Padova

RTAI

RTAI

Real Time Application Interface by Dipartimento di Ingegneria

Aereospaziale dell’Università di Milano (DIAPM)

© Antonio Barbalace 2008 RTOS - RTAI course 3

DEI Universit

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RTAI

• It is not a complete RTOS

• It makes Linux kernel fully pre-emptable

• Some (limited) changes must be applied to the kernel, i.e. interrupt handling and scheduling policies

• RTAI acts essentially as an interrupt dispatcher • RTAI consider Linux as a background task

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RTAI

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RTAI

History and evolution (1/2):

• At first it was PCDOS-DIAPM-RTOS (16bits real mode);

• Then it was implemented in 32 bits real/protected mode;

• Approaching Linux (2.0.25);

• NMT-RTL appears and goes on DIAPM-RTL variant was born

• RTHAL-RTAI patch for 2.2.xx kernel ready (beginning 1999)

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RTAI

History and evolution (2/2):

• April 1999 first version of RTAI for UP and SMP; • Jan 2001 NMT-RTL now RTLinux was patented; • Jun 2002 ADEOS was firstly released;

• ADEOS substitutes RTHAL and from now on no patent problems;

• LXRT scheduler was introduced; • More than one branch of RTAI;

• October 2005 Fusion branch becomes a stand-alone distribution Xenomai;

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RTHAL

• To encapsulate all the data structures and time critical functions of the kernel in one defined structure

• All the original operations work through RTHAL pointers

• RTHAL pointers are dynamically modifiable ⇒ RTAI can be selectively activated/disactivated • Successively substituted by (a modified version

of) ADEOS

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ADEOS

Adaptive Domain Environment for

Operating Systems

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ADEOS

Dual-kernel approach

Nano kernel

Open source

NEW NAME:

ADEOS/ipipe

CHANGES:

• Functions name

• Various improvements

ADEOS

Dual Kernel with ADEOS/ipipe nano kernel

Hardware ADEOS/ipipe Linux RTOS

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ADEOS

Many different OS (or multiple instances of the same OS) running on the same machine, sharing the same hardware.

OS User Process 1 User Process 2 User Process 3

Hardware

Hardware OS User Process 2

User Process 1 User Process 3

Hardware ADEOS/ipipe OS 2 OS 1 OS 3 User Process 1 User Process 2 User Process 1 User Process 2 User Process 3 User Process 1 User Process 2 co-DOS era OS era ADEOS era

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ADEOS

Basics:

• Domains

• Pipeline

• Interrupts

• Events

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ADEOS

- Resource virtualization layer available as a Linux kernel patch/module

- It enables multiple

domains

- A domain is generally a complete OS but no assumption is made by Adeos on the

sophistication of a domain

- Domains compete for processing external events (interrupts) or internal ones (traps)

- It exports a generic, CPU-independent API to client domains

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ADEOS

4 ADEOS communication methods

A – general usage of the hardware made by a domain

B – Adeos receives control from the hardware (through HW o SW interrupts) C – Two-ways communication (the domain is aware of the presence of Adeos) D – Invoking of an OS’s interrupt handler (the domain could not be aware of

the presence od Adeos)

OS domain 1 OS domain 2 ADEOS Hardware C D A A B

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ADEOS event pipeline

- A domain can ask ADEOS to be notified of:

- Every incoming external interrupt or auto-generated virtual interrupt

- Every system call issued by applications

- Other system events triggered by the kernel code (task switching, signal notification, task exit, etc.)

- Events are dispatched by ADEOS in orderly manner assigning a static priority to each domain

- Active domains are orderly queued into a

pipeline

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ADEOS

ADEOS/ipipe interrupts/events pipeline (on interrupt) Root domain OS domain 3 OS domain 2 OS domain 1 OS domain n OS domain idle wired? Hardware Interrupt Linux

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ADEOS

• Maskable (a domain could be stalled) • Propagated down the pipeline

• Logged (Optimistic interrupt protection scheme)

– A domain can temporarily stall its stage in the

pipeline

– In this state an incoming interrupt is not delivered to the domain’s handler, is logged, and is not flowed down to the lowest priority domains

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ADEOS

• Raised mostly for software cause • Non maskable

• Propagated from the source domain up the pipeline

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ADEOS

References:

• Karim Yagmour et others (OperSys Inc)

• www.adeos.org

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RTAI/ADEOS

- RTAI is installed as domain with the maximum (relative) priority, higher than the Linux domain ⇒ RTAI serves interrupts before Linux

Standard processes Linux kernel RT processes

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RTAI VS Xenomai

RTAI immediate dispatching Xenomai

RTAI pipeline (no immediate dispatching) asm low-level Linux Hardware ADEOS/ipipe Linux Xenomai asm low-level Linux Hardware ADEOS/ipipe Linux RTAI DEI Universit y of Padova

RTAI VS Xenomai

Currently ported on: • ARM

• I386, ia64 (SMP, MUP) • PowerPC Run: • Kernel • User Main goal : • Fast dispatching API interface: • RTAI • Posix 1003.1b • RTDM Xenomai

Currently ported on: • ARM • i386, ia64 (SMP) • PowerPC, PowerPC64 (SMP) • Blackfin Run: • Kernel • User Main goal : • Portability API interface: • Xenomai native • Posix 1003.1b • RTAI • VxWorks • pSos+ • VRTX • uITRON • RTDM

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RTAI VS Xenomai

LESS INTEGRATION PROBLEMS: Xenomai

BETTER PERFORMANCE: RTAI (immediate dispatching)

EASY APPLICATION PORTING: Xenomai

DEBUGGING SUPPORT: Both

CLEAR, AND WELL ORGANIZED SOURCE CODE: Xenomai

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RTAI

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RTAI

RTAI

• Immediate Interrupts dispatching

• Interrupt registering/deregistering functions • PIC management routines

• Hardware Timers (8254/APIC) management routines • registering/deregistering timers handler functions • Trap handlers registering/deregistering functions • Provides rt_printk/rt_synch_printk

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RTAI

8254

Native RTAI timer; it supports at least two modes that are used: • Periodic Mode

• Oneshot Mode This timer is used in: • UP

• SMP

Counter 0 shared with Linux.

APIC

At first used with multiprocessor hardware only. Same modes: • Periodic Mode • Oneshot Mode Used in: • SMP • MUP ADEOS/RTHAL timers

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RTAI

Periodic Mode

Automatic timer register reload

Oneshot Mode

Compulsory timer register update

timer_handler{ ... } timer_handler{ ... } timer_handler{ ... } timer_handler{ ... } Timer update timer_handler{ ... } timer_handler{ ... } timer_handler{ ... } timer_handler{ ... } Timer update

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RTAI

• Task creation/destruction routine • Task suspend/yield/sleep routine • Task Timer related function

• Scheduling disciplines/policy

• LXRT Linux (user space) Real-Time capability • Task interface with IPC mechanisms

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RTAI

Scheduler

Scheduling policy:

• RMS

• EDF

• FIFO, default scheduler

• RR

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RTAI

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RTAI

Scheduler

LXRT

Scheduler kernel

Scheduler user

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RTAI

• Bits (a sort of signals) • Fifo

• Message • Mailbox

• Message queue

• NetRPC (now requires RTNet) • Semaphore • Shared memory DEI Universit y of Padova

RTAI

RTAI References:

Paolo Mantegazza, DIAPM

www.rtai.org

Xenomai References:

www.xenomai.org